Dodge rating is almost always better than parry rating. One, as a DK tank, you tend to have a generous amount of parry from things like forceful deflection, so you hit DR faster. Two, parry rating converts to a % at a worse rate than dodge rating. 1% dodge = 39.35 dodge rating, but 1% parry = 49.18 parry rating.
There is a point at which parry is better than dodge, but if memory serves, it's obscenely high. Just go with the dodge.